Corrugated paperboard is currently used in countless packaging applications and is, by far, the most popular packaging for articles or materials suitable for packaging in boxes, whether for shipment, storage or both. Because of commercial value, the conventional corrugated paperboard container has been the focus of extensive research and development resulting in continuous improvements therein. Of late, much effort has been put into developing containers with improved stacking strength as well as deriving more strength from less fiber mass.
Of particular interest herein is the fact that loads and stresses placed on corrugated packages are rarely distributed uniformly. This can be due to many different reasons; uneven weight distribution of package contents, shape of package contents, handling (or mishandling), etc. Whatever the cause, the result is often loads and stresses that are highly concentrated or localized. Industry has sometimes addressed this issue by improving package design, often times quite creatively. However, good design and engineering practices dictate that a package be manufactured to perform in a “worst case” scenario, so the inevitable result is a package which meets the stringent performance requirements of certain areas while providing excessive packaging in others. Importantly, this results in a package that is not as economical or cost effective as it could be.
For example, one of the most critical performance criteria for many corrugated paperboard boxes is stacking strength. Box designers typically increase stacking strength by increasing the weight of the liners and/or medium. This provides the added stacking strength needed in the walls of the box, but also provides additional strength (and fiber mass) in the top and bottom of the box where it is not needed, unnecessarily increasing cost.
Another example involves packages that need to be bulge and/or burst resistant due to outward force applied by the package contents, often a fluid material. Like the stacking strength example supra, a common remedy to this problem is simply making a box out of heavier components. This remedy may solve the problem, but is uneconomical. A common post-manufacturing remedy to this problem consists of simply applying a reinforcing tape, such as a nylon mesh reinforcing tape, to the external surface of a package. This remedy is cumbersome, costly due to the labor involved, often provides sub-optimum performance, typically not an option if aesthetics are an issue, and adds little to prevent package deformation. Methods are available wherein a reinforcing mesh and or strands are included between the medium and outside liner, but these remedies provide reinforcement to the entire package including areas where reinforcement is unnecessary.
Yet another example involves packages which include closure flaps that are subject to repeated opening and closing. These packages often fail at the closure scoreline. A common remedy is to apply reinforcing tape along the scoreline. As with the bulge resistant example above, this remedy is cumbersome, costly due to the labor involved, often provides sub-optimum performance, and is typically not an option if aesthetics are an issue.
A final example involves large appliances packaged in regular slotted containers with a basiloid flap at the upper end. In this application, lift trucks fixed with a flat, laterally situated lifting hook, lift and move these loaded containers by inserting the flat hook into the space between the container sidewall and basiloid flap then lifting the entire package by the flap. This method of transport places highly localized loads on the basiloid flap/joint area and has resulted in failure within the joint, specifically along lateral scorelines. This problem has been remedied by either applying reinforcing tape around the joint area or increasing the basis weight of the components in the container. The former requires additional labor and provides sub-optimum performance, while the latter unacceptably increases packaging costs.
Many technologies and methods are known that enable the manufacture of reinforced packages, specifically reinforced corrugated paperboard packages, but each have limitations which fall short of the benefits provided by this invention.
U.S. Pat. No. 4,398,650 to Holmes et. al. discloses a corrugated container wherein a plurality of reinforcing strands are contained between the medium and outside liner. The enhancement provided by this method is limited to bulge and burst resistance. It adds little in terms of stacking strength, rigidity or scoreline integrity.
U.S. Pat. No. 5,285,957 to Halsell discloses a reinforced corrugated container wherein a reinforcing mesh composed of natural cellulosic strands is contained between the medium and outside liner. As with the Holmes patent listed above, the enhancement provided by this disclosure is limited to bulge and burst resistance. This method provides no additional stacking strength, rigidity or scoreline integrity, and is not selectively applied.
U.S. Pat. No. 4,437,850 to Ono discloses a process of manufacturing reinforced corrugated cardboard type containers wherein a reinforcing agent is applied along longitudinal scorelines between the outside liner and medium. In this disclosure, the lines of reinforcing agent are located such that they cover the areas that are scored and ultimately become the upper and lower horizontal perimeter of a finished box. As disclosed, this method enhances stacking strength by minimizing crush failure in the vicinity of the treated scorlines, but adds no stacking strength to the walls or additional resistance to bulge or burst. Most importantly, this method requires that scoring, folding and forming occur before the reinforcing agent hardens.
U.S. Pat. No. 3,411,689 to Brackett discloses placing narrow strips of thermoplastic material into corrugated board flutes at intervals and before the corrugated medium is attached to a second liner.
U.S. Pat. No. 3,796,307 to McKinney discloses a heat shrinkable polymeric film attached to corrugated fluting, the resulting product is formed into a carton or bundled package and then the entire package is heated to shrink the polymeric film.
U.S. Pat. No. 4,936,451 to Shuert is directed to a container comprised of a sleeve and end unit. The sleeve is made of corrugated material and contains a plurality of slots which interlock with latches on the end unit.
Canadian Pat. No. 889808 to Karass discloses a “weftless” tape or strap product. The tape is comprised of threads of synthetic resin, including polyethylene. An adhesive is then applied to the threads.
U.S. Pat. No. 3,406,052 to Mendham is directed to waterproof containers that maintain strength. This is accomplished by passing corrugated fiberboards through heat-softened films of thermoplastic material (including polyethylene) and then applying a certain amount of pressure to adhere the films to the faces of the fiberboard. The edges of the coated fiberboards are crushed and then sealed with a waterproof substance.
U.S. Pat. Nos. 4,095,692 and 4,177,895 both to Shelton are directed to a container having walls laminated with polymeric film, including polyethylene. The purpose of the lamination or “shroud’ of polymeric film is to prevent air current from passing through the interior of the container.
The present invention is an improvement over prior art processes by providing reinforcing packaging strips to strengthen the load-carrying joints in corrugated packaging by selectively applying the strips to desired areas. Further, in addition to increasing strength, the strips provide more tear resistance to the reinforced joint and stiffen the entire flap, enabling it to carry a heavier load without failing.
Typically, corrugated paperboard is manufactured such that the finished product includes two opposed liners, a fluted medium disposed in between with adhesive forming permanent bonds between the flute tips and the opposed liners. Corrugated paperboard that includes two liners about one medium is typically called single wall. The term double wall typically describes three liners and two mediums in alternating layers, while triple wall refers to alternating layers including four liners and three mediums.
In general, to manufacture single wall corrugated paperboard, three substrates are used, a singleface liner, a doubleface liner, and a corrugating medium, and several manufacturing steps are followed. First, a continuous web of corrugating medium is directed between two corrugating rolls that form the medium into a corrugated web with lateral flutes. Next, the fluted medium is directed against a glue-bearing cylinder that places a metered amount of adhesive on each flute tip of one side.
The medium is then directed against a continuous web of singleface liner such that the glue-bearing flute tips bond evenly to the liner to form a substrate commonly called singleface-corrugated paperboard. The singleface-corrugated paperboard is then directed against a second glue-bearing roll that places a metered amount of adhesive on the flute tips located opposite the singleface liner which is then directed against a continuous web of double-face liner such that the glue-bearing flute tips bond evenly to the doubleface liner to form single wall corrugated paperboard (commonly referred to as combined board).
The next step in the manufacturing process involves moving the web of combined board through a controlled hot plate section in order to heat and cure the adhesive. Upon exiting the hot plate section, the web travels through a cooling section wherein ambient air cools the paperboard and adhesive. The web is then directed through a slitter/knife section wherein the combined board is continuously slit longitudinally, then laterally cut into sheets suitable for converting into boxes or other finished containers. Double and triple wall combinations are manufactured in the same general way except that two or three layers of single-face corrugated are directed together along with a doubleface liner. The steps involved in manufacturing corrugated paperboard are highly standardized throughout the packaging industry and well known within the art. However, these known processes are not entirely satisfactory in certain applications such as in strengthening load-carrying joints in corrugated packaging and enhancing tear resistance to movable joints in corrugated packaging.
The invention disclosed herein addresses the problems discussed above and the shortcomings of currently available remedies. A general object of the present invention is to provide reinforcing strips made of a paper substrate coated on one side with low melt, low density polyethylene for application to selected portions of corrugated paperboard structures.
Another object of the invention is to provide a method for manufacturing reinforced corrugated paperboard packaging that is more economical over the prior art method of reinforcing which uses nylon-based tape.
A further object of the invention is to provide a method for manufacturing reinforced corrugated paperboard packaging wherein reinforcement can easily be applied only to select areas.
A specific object of the invention is to provide an apparatus for manufacturing selectively reinforced corrugated paperboard.
Another specific object of the invention is to provide a method for manufacturing selectively reinforced corrugated paperboard that is compatible with existing manufacturing equipment and requires no modification of major equipment.
Another object of the invention is to provide a method for manufacturing selectively reinforced corrugated paperboard that utilizes a heat-activated adhesive that is activated by ambient heat present in a conventional hot plate section.
A further object of the invention is to provide a method for manufacturing selectively reinforced corrugated paperboard that remains formable and pliable after manufacturing.
Another further object of the invention is to provide a stronger corrugated box structure by stiffening the folding flap with reinforcing strips.